Don't count your chickens before they vest, in 6 months somebody might be getting them at $90
He got the offer and decided on his start date way back in August of last year so any luck he happens by is good luck. He could've chosen to be luckier if the stock price goes down further, but I'd say this is pretty lucky as it is already for something he can't control.
Edit: ignore the tax part, I think I'm wrong there.
That said, I think Microsoft still does a 1-year cliff, so they won't have anything to sell for a year anyway.